Thread: Chris Hall's Carpentry Study Group - Fifth Project

I get an Invalid attachment message for the links. No pics

Ok - Think I've fixed it now...

Yxoc,

Love to see this kind of work. Well done. Keep it coming.

Regards,
Gadge

G'Day Gary,
Thanks very much for your interest.

Incidentally I am keen to know what projects you are up to these days, I've been meaning to get over to the hms forums and see what's going on but life is busy...

warm regards

Derek

Hi Derek,

Haven't done a thing lately. I bought a new home which has taken a lot of my time plus my two school age boys live with me now after my wife and I separated a couple years ago. I reckon it'll be some time before I have the luxury of doing any woodwork. For the time being I'll do my woodwork vicariously by seeing the projects you and others create.

Regards,
Gadge

Gary,
Sorry to hear about your family circumstances.

I understand your pain - I have two young school age children. After the first child, the 'me' time was significantly curtailed, after the second, well, nearly everything stopped... I wouldn't change anything of course but that may explain while my photos are always dark - woodwork projects are only getting worked on in the late hours.

I would be glad if my projects provide a small amount of vicarious joy for you and others. Hopefully this project will progress a little more steadily from now.

You often come to mind when I'm sharpening...

Regards

Derek

Thanks Derek.

Regarding sharpening stones, I'm not sure if I told you before but I have some reasonably good examples of Aussie home grown sharpening stones. They are from the same areas as the one you have however I found another deposit which is a little finer and is good for final honing. Let me know if you want one as I could send it to you.

Regards,
Gadge

Gadge,
Well I'm very interested of course. I use the first stone you gave me constantly - I find it gives a finer finish than my 8000 grit stone, and there is definitely a difference in the quality of finish between a natural and synthetic stone.

I insist on sending something in return though - bottle of wine, or beer?

Cheers

Derek

OK Derek, you're on.

A bottle of wine for an aussie toishi. I'll contact you offline to discuss address etc and might come out to Richmond for a drive.

Regards,
Gadge

A quick update,
I have recut the dodgier side of the mitre joint and am just ruminating on a better way to drill the holes (I don't want to have to do it a third time). In the mean time, the next item we will work on will be the wall plate or keta. As you may remember I cut the major components only roughly to size so I have been working on bringing them down to final dimensions. The closest piece in the photo is now correctly dimensioned at 120mm by 90mm. The other piece is next. On the floor is the evidence.
20130314_175039.jpg

Well it has been a long time between drinks on this thread - nearly a year in fact. If you thought I had lost interest, then fear not, merely other areas of life encroaching more than I might like.

If you have forgotten what this thread was about, it is a study group started by Chris Hall (his blog here), that one may join via subscription. The purpose of the group is to study Japanese carpentry by constructing models that deal primarily with compound joinery, as used in Japanese built structures (wooden ones of course). The latest model is a corner of a regular hipped roof - it looks like this:
finishedmodel.jpg
(As an aside, all sketch up graphics used in this thread, unless I say otherwise, are extracted from mailings sent out by Chris)

As you can see the main structural components visible are the wall plates (Keta), the hip rafter (Sumigi) and the jack rafters that branch off the hip rafter. The red coloured board is called the Hirokomai and this was the last component I completed.

The main area of study in this piece is the three way lap joint that is used at the junction where the two wall plates and the hip rafter intersect. Additionally, this lap joint sits atop a post and the tenoned end of the post penetrates and ties together all three pieces. A close look at the picture above will show that the two wall plates intersect at right angles. The hip rafter however is at 45 degrees to these pieces and also slopes at an angle to the horizontal. Note that the slope of the hip rafter is different to the slope of the common and jack rafters.

A shortened stub post is used in the model and with its tenoned end, will look like this:
steppedtenon.png
The full width portion of this tenon will be housed in the lower half of the Keta lap, the top half will have only the square section housed within. Here is the completed piece, ready to be rudely thrust into the other joint components:
P1020253.JPG
Ignore the spare piece on the right that failed to rise to the occasion.

On one of my last posts I showed the Keta pieces correctly dimensioned. A little extra work is now required to shape the nose of each piece and cut small trenches where the jack rafters will be housed:
DSCF1036.jpg

The principal aim of the three way lap joint is to make the joint as strong as possible by taking away as little 'meat' from each piece as possible. To this end the joint is designed so that each piece gives up a little bit of its thickness, and in this way, the weakening of each member is shared. If all pieces sat in the same plane this would be simple; we would take a third of the thickness from each. That is not the case however, as the hip rafter trenches through the Keta pieces at a slope. This means that the material left beneath the hip is also sloped and the joining surfaces between the Keta pieces is sloped as well. Sounds complicated? Maybe a diagram will help:
exploded_lap.png
The hip rafter has been removed in this diagram but a dark blue shaded area indicates where it passes. In this graphic the hip would be sloping down towards the viewer. Hopefully you can see that the remaining wood below the dark blue 'print' of the hip rafter is then divided evenly (via a sloping surface) between the two Keta pieces. When cut correctly (including a trench where the hip rafter passes through) and brought together, the Keta joint would look like this:
assembled_lap_tenon.png
Note again the tenoned post that will pass through all three pieces.

The all important marking out comes next:
DSCF1035.JPG

The lines are quite faint - this piece will be the top half of the Keta lap. Hopefully you can see a set of plumb lines where the other Keta piece will cross at right angles and then a set of lines, sloping at 45 degrees to the surface, that indicate where the hip rafter will pass through. Within the plumb lines and just barely visible is a sloped line that will be the mating surfaces between the two Keta pieces - there is a lot of wood to be cut away from this piece and that will happen next.

Ok, despite showing you the layout on the top piece I have started cutout on the bottom piece, this means a lot of wood needs to be removed from above the lap surface. Before that can happen however, I need to first cut the mortice for the stepped tenon. This is best done now while there is still wood supporting the chopping. In this piece the mortice starts as a 30mm by 68mm rectangle. After a depth of 30mm it steps down to a 30mm by 30mm square section:
DSCF1040.jpg

I can strongly recommend the mortice chisels by Narex, they pretty much chop the mortice by themselves.

I only took the square section hole deep enough to ensure it reached the lap surface:
DSCF1042.JPG

With the mortice complete, the lap cutout can commence:
DSCF1134.JPG

No turning back now! At this point, anxiety about cutting to the wrong line reaches its peak.
Assuming all is well though, we can continue:
DSCF1046.JPG
I am a conservative sawyer so some paring is required to get to the line and a square paring block is pressed into service to assist in this matter. Here you can see the 30mm square exit hole of the mortice that was chopped from the other side:
DSCF1050.JPG
You will agree that a lot of thickness is lost in this piece - this is mitigated by the post that will support from underneath.

Great thread and a very interesting detail.
Are you planning to build a full size structure in the future or just enjoying the woodwork ?
Is that joint something standard or a special shrine/temple joint ?

Keep the posts coming !

Sam